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This module provides access to the Unicode Character Database (UCD) which
defines character properties for all Unicode characters. The data contained in
this database is compiled from the UCD version 12.1.0.

The module uses the same names and symbols as defined by Unicode
Standard Annex #44, “Unicode Character Database”. It defines the
following functions:

Return the normal form form for the Unicode string unistr. Valid values for
form are ‘NFC’, ‘NFKC’, ‘NFD’, and ‘NFKD’.

The Unicode standard defines various normalization forms of a Unicode string,
based on the definition of canonical equivalence and compatibility equivalence.
In Unicode, several characters can be expressed in various way. For example, the
character U+00C7 (LATIN CAPITAL LETTER C WITH CEDILLA) can also be expressed as
the sequence U+0043 (LATIN CAPITAL LETTER C) U+0327 (COMBINING CEDILLA).

For each character, there are two normal forms: normal form C and normal form D.
Normal form D (NFD) is also known as canonical decomposition, and translates
each character into its decomposed form. Normal form C (NFC) first applies a
canonical decomposition, then composes pre-combined characters again.

In addition to these two forms, there are two additional normal forms based on
compatibility equivalence. In Unicode, certain characters are supported which
normally would be unified with other characters. For example, U+2160 (ROMAN
NUMERAL ONE) is really the same thing as U+0049 (LATIN CAPITAL LETTER I).
However, it is supported in Unicode for compatibility with existing character
sets (e.g. gb2312).

The normal form KD (NFKD) will apply the compatibility decomposition, i.e.
replace all compatibility characters with their equivalents. The normal form KC
(NFKC) first applies the compatibility decomposition, followed by the canonical
composition.

Even if two unicode strings are normalized and look the same to
a human reader, if one has combining characters and the other
doesn’t, they may not compare equal.

This is an object that has the same methods as the entire module, but uses the
Unicode database version 3.2 instead, for applications that require this
specific version of the Unicode database (such as IDNA).